1. Field of the Invention
The present invention relates to an array type ultrasonic probe constructed by arraying a plurality of piezoelectric elements on a backing material, and more particularly it relates to an array type ultrasonic probe having an improved acoustic field characteristic and a method of manufacturing the same.
2. Description of the Related Art
The array type ultrasonic probe is used as a unit for transmitting and receiving an ultrasonic wave in ultrasonic diagnostic equipment for a medical purpose and so on, in order to obtain a tomogram of an examinee, i.e., to obtain a tomogram in vivo. When obtaining a tomogram, a plurality of piezoelectric elements constituting the array type ultrasonic probe are driven by a linear scan method or a sector scan method. In recent years, it has been desired to provide an array type ultrasonic probe having a good acoustic field characteristic of ultrasonic wave, which is transmitted and received, together with an excellent producibility thereof.
FIGS. 1 and 2 are cross-sectional and plan views of an example of a conventional array type ultrasonic probe, respectively.
The array type probe is constructed by arranging a plurality of piezoelectric elements 2, each having upper face electrode 1a and lower face electrode 1b , on backing material 3. In the illustrated one, a plurality of piezoelectric elements 2, each having a rectangular shape, are arranged in an array in a direction in which the short sides of piezoelectric elements 2 are extended. In a central region of the upper face of each piezoelectric element 2, acoustic matching layer 4 for matching acoustic impedance thereof with an examinee under ultrasonic diagnosis is formed. Also, non-illustrated acoustic lens is formed on acoustic matching layer 4. Further, on the opposite end portions of respective upper faces of piezoelectric elements 2, lead wires 5a and 5b are connected by soldering for providing joints among the plurality of piezoelectric elements 2, and by lead wires 5a and 5b, respective upper face electrodes 1a are commonly connected together to become earth potential. To lower electrodes 1b of respective piezoelectric elements 2, metal foils 6 for the purpose of leading out an electrode are connected in such a manner that they are alternately disposed and connected to one of the opposite ends of the elements 2, and electric driving voltages for respective piezoelectric applied to metal foils 6.
Nevertheless, in the above-described array type probe, ultrasonic wave is radiated from the opposite end portions of piezoelectric elements 2, to which lead wires 5a and 5b are connected, and the radiated ultrasonic wave interferes with the ultrasonic wave radiated from acoustic matching layer 4 to result in causing a problem such that an adverse affect is provided on the acoustic field characteristic.
Thus, in an array type probe as illustrated in FIG. 3, on one end portion of respective piezoelectric elements 2, lower face electrodes 1b are turned up toward the upper face the elements, and on the other end portion of respective piezoelectric elements 2, upper face electrodes 1a are turned down toward the lower face. Furthermore, metal foils 6 for earthing are connected to one end portion of the lower faces of respective piezoelectric elements 2, and metal foils 6 for drive signal are connected to the other end portion of the same lower faces. As a result, in the array type probe of this type, respective of the opposite end portions in the longitudinal direction of piezoelectric element 2, in which no acoustic matching layer 4 is arranged, are in a condition where the upper and lower faces thereof are in an identical electric potential, and therefore radiation of the ultrasonic wave is prevented.
In the meantime, in manufacturing piezoelectric element 2, upper electrode 1a and lower electrode 1b are formed on a piezoelectric body, and thereafter a process is needed to apply a high electric voltage across upper and lower electrodes 1a and 1b for polarizing the piezoelectric body. In the probe illustrated in FIG. 3, since turn-down portion 1c of upper face electrode 1a and an end of lower face electrode 1b confront one another on the lower face of piezoelectric element 2, during the polarizing process, lest electric field more than necessity might be applied to this confronting portion, it is usually necessary to provide spacing more than a predetermined extent, i.e., an extent equal to or more than the thickness of the piezoelectric body, between turn-down portion 1c and the end of lower face electrode 1b. Similarly, spacing equal to or larger than a predetermined extent should be provided between turn-up portion 1d of lower face electrode 1b and an end of upper face electrode la on the upper face of piezoelectric element 2. Thus, a problem has occurred in that an effective length of the central region of piezoelectric element 2, except for the turn-down and turn-up portions, must be made short. Further, since the upper and lower face electrodes provided with turn-down and turn-up portions, respectively, are formed, an effective length of the ultrasonic wave generative face is in turn preset beforehand, and accordingly a problem has occurred in that degree of freedom of design is narrowed.
An object of the present invention is to provide an array type ultrasonic probe, which enables it to prevent radiation of ultrasonic wave from end portions of piezoelectric elements as well as to extend degree of freedom of design by prolonging an effective length of the piezoelectric element.
Another object of the present invention is to provide a method of manufacturing an array type ultrasonic probe, which enables it to prevent radiation of ultrasonic wave from end portions of piezoelectric elements as well as to extend degree of freedom of design by prolonging an effective length of the piezoelectric element.
The above-described object of the present invention can be achieved by an array type ultrasonic probe, which comprises a backing material; a plurality of piezoelectric elements arranged on and fixedly secured to the backing material, each piezoelectric element having a first end portion, a second end portion opposing the first end portion, a first major face facing the backing material, a second major face, a lower face electrode formed on the first major face, and an upper face electrode formed on the second major face; a first conductive member for electrically connecting the lower face electrode and the upper face electrode at the first end portion; and a second conductive member for electrically connecting the lower face electrode and the upper face electrode at the second end portion; wherein the first major face is formed, along the first end portion, with a first notch portion to thereby electrically separate the lower face electrode, and the second major face is formed, along the second end portion, with a second notch portion to thereby electrically separate the upper face electrode.
The above-described another object of the present invention is achieved by a manufacturing method of an array type ultrasonic probe having a backing material and a plurality of piezoelectric elements arranged on the backing material, which comprises the steps of fixedly securing a piezoelectric plate formed thereon with an upper face electrode and a lower face electrode to the backing material by a first conductive adhesive so that the lower face electrode faces the backing material; forming a first slit running from the upper face electrode to the backing material, relative to a first side of the piezoelectric plate; fixedly securing an acoustic matching layer onto the upper face electrode by a second conductive adhesive while electrically connecting the upper and lower face electrodes by the second adhesive at the first side and a second side of the piezoelectric plate, the second side opposing the first side; forming a second slit running from an upper face of the acoustic matching layer to the piezoelectric plate while separating the upper face electrode, relative to the second side of the piezoelectric plate; and thereafter separating the piezoelectric plate into individual piezoelectric elements.
The above-described another object of the present invention is also achieved by a manufacturing method of an array type ultrasonic probe having a backing material and a plurality of piezoelectric elements arranged on the backing material, which comprises the steps of fixedly securing a piezoelectric plate formed with upper and lower face electrodes together with a first groove separating the lower face electrode on a first side of the piezoelectric plate, and a second groove separating the upper face electrode on a second side of the piezoelectric plate, to the backing material in a manner such that the lower face electrode faces the backing member, by applying insulating adhesive to a central region of the backing material, the second side opposing the first side; applying insulating adhesive to a central region of the upper face electrode and conductive adhesive to the regions of the upper face electrode to thereby fixedly secure an acoustic matching layer onto the upper face electrode while electrically connecting the upper and lower face electrodes by the conductive adhesive at the first and second sides of the piezoelectric plate; and thereafter separating the piezoelectric plate into individual piezoelectric elements.
In the present invention, the lower and upper face electrodes of the piezoelectric plate are separated by the first and second notches provided along the opposite end portions of the piezoelectric plate. The lower and upper face electrodes are connected by the conductive material at each end portion of the piezoelectric plate. Therefore, the opposite end portions of the piezoelectric plate are made to have an identical electrical potential, so that radiation of the ultrasonic wave from the end portions of the piezoelectric elements can be prevented. Also, since the notches are formed after the polarizing processing, width of each notch may be the smallest. Further, the first and second notches may be formed at any arbitrary positions, and accordingly the effective length of the respective piezoelectric elements may be determined in compliance with requested specifications.